Advancement of digitization of audio visual equipment over the recent years has made it possible to copy content without quality deterioration. However, unlimited copying of copyrighted content could infringe the right to which the copyright holder is entitled. Therefore, there is a demand to have a proper copyright protection function for audio visual equipment.
As copy control in digital audio equipment, a serial copy management system (hereinafter abbreviated as “SCMS”) has been widely used from around the 1980s. In the SCMS, copy control information is recorded together with content in a medium such as a CD, a minidisk (MD) and an airwave. When the content is to be copied with a connection established inside the same housing or between different pieces of equipment via a digital interface, whether to permit copying is controlled in accordance with the copy control information of the content. The SCMS is effective to a certain extent, as in the case of commercial recording machines, such as those for MDs.
The SCMS however requires that the copy control information is held as digital data which is independent from the content. This allows neither transmission of the copy control information during analog transmission, nor copy control. Further, when a personal computer or the like is used, the copy control information can be easily nullified.
In light of these problems with the SCMS, the Content Protection for Prerecorded Media standard and the Content Protection for Recordable Media standard (hereinafter abbreviated as “CPPM” and “CPRM”) which are copyright protection systems utilizing the DVD and the SD (Secure Digital) Memory Card Audio standards (hereinafter abbreviated as “SD Audio”) adopt a copy control method which uses an electronic watermark. Meanwhile, copy control/playback control methods which use electronic watermarking have been proposed for the SDMI (Secure Digital Music Initiative) standard determined involving the music industry, the computer industry, the consumer electronics industry and the like.
Even when a signal in which an electronic watermark is embedded is played back, one cannot recognize a difference between this signal and the original signal while viewing normally. Thus, the quality of the content does not deteriorate. Since an electronic watermark is embedded directly in the content, copy control information can be transmitted even during analog transmission. An electronic watermark also has durability so that copy control information is maintained even after ordinary audio compression and expansion (e.g., MP3). In addition, without special embedding and a special decryption apparatus, an electronic watermark can not be read or written. When combined with encryption of content itself, an electronic watermark can realize more powerful copy control than the SCMS.
By means of electronic watermarking technologies for use in CPPM, CPRM and SDMI, it is possible to embed 12-bit information as an electronic watermark within digital audio data of the linear PCM format. Of this, two bits are used for copy control. The two bits express the three states: “copy_freely”; “copy_one_generation” and “no_more_copy”. Although these two bits, as such, can express four states, use of the remaining one is prohibited.
An electronic watermark is detected through predetermined signal processing of digital audio data of the linear PCM format for a predetermined period of time (which is fifteen seconds in the case of SDMI, CPRM and CPPM). In the event that content has been compressed as MP3 or the like, an electronic watermark is detected after decoding into linear PCM. Even an analog signal, when converted into linear PCM using an AD convertor, permits detection of an electronic watermark.
As for the detection of an electronic watermark, there are two results. First, is that an electronic watermark is detected. Second, is that an electronic watermark is not detected. Upon detection of an electronic watermark, the three states of “copy_freely”, “copy_one_generation” and “no_more_copy” are distinguished from each other.
In relation to playback control utilizing conventional electronic watermarking, Japanese Patent Application Laid-Open Gazette No. 2001-229612 titled “COPY CONTROL METHOD FOR DIGITAL DATA AND OPTICAL DISK PLAYBACK APPARATUS” for example describes an optical disk playback apparatus (pages 7 through 13, and FIGS. 6 and 12). This optical disk playback apparatus will now be described as a first conventional technique. This optical disk playback apparatus is an apparatus complying with the CPPM control method.
The entire disclosure of Japanese Patent Application Laid-Open Gazette No. 2001-229612 is incorporated herein by reference in its entirety.
While describing playback control in the following, copy control information embedded in a content using electronic watermarking will be referred to as watermark CCI. In contrast, copy control information recorded as digital data in an optical disk, independent of content, will be referred to as digital CCI. Digital CCI and watermark CCI in an optical disk demand playback control as shown in FIG. 7.
In FIG. 7, digital CCI is added to an encrypted content, and in accordance with the value of the digital CCI, a player performs playback control as described below. Encrypted recording of a copy-free content, namely, a content bearing digital CCI of 00 is prohibited. Hence, a content which has been encrypted but bears digital CCI of 00 is regarded as an unauthorized content, and playback is restricted. Meanwhile, when the digital CCI is 10, that is, in the case of restricted copying (copy_one_generation), the player plays back in a normal manner. The player plays back in the normal manner also when the digital CCI is 11, that is, in the case of prohibited copying.
On the contrary, when content has not been encrypted, in accordance with the value of watermark CCI, the player performs playback control as follows. First, when the watermark CCI is 00, that is, in the case of free copying, the player plays back in the normal manner. Meanwhile, when the watermark CCI is 10, that is, in the case of restricted copying (copy_one_generation), the player restricts playback. The player restricts playback also when the watermark CCI is 11, that is, in the case of prohibited copying.
FIG. 8 is a block diagram of an optical disk player which uses a conventional copy control method. The optical disk player 174 is comprised of a spindle motor 161, an optical pickup 162, a mechanism control part 163, a signal processing part 164, an encryption/decryption apparatus 165, a digital CCI decryption apparatus 166, an audio visual decryption apparatus 167, a watermark CCI decryption apparatus 169, a DA convertor 168, a digital signal output control part 170, an analog signal output control part 171, a display part 172 and a system control part 173.
The spindle motor 161 rotates a disk 160. The optical pickup 162 reads a signal recorded on the disk 160. The mechanism control part 163 drives and controls the spindle motor 161 and the optical pickup 162. The signal processing part 164 retrieves data out of an output from the optical pickup 162 or executes error correction to thereby extract a system stream and supplies a control signal to the mechanism control part 163. The signal processing part 164 also analyzes the system stream, extracts playback style information which is indicative of the start and the end of a playback unit, the end of playback of a whole disk, etc., and sends to the system control part 173. The encryption/decryption apparatus 165 checks whether the system stream has been encrypted and in the event that the system stream has been encrypted, decrypts the cipher. The encryption/decryption apparatus 165 also provides the system control part 173 with encryption status information which expresses whether the system stream has been encrypted. The digital CCI decryption apparatus 166 detects digital CCI out of an unencrypted system stream output from the encryption/decryption apparatus 165. The audio visual decryption apparatus 167 extracts a digital audio signal or digital video signal out of an unencrypted system stream output from the encryption/decryption apparatus 165 and performs decoding. The watermark CCI decryption apparatus 169 detects watermark CCI data out of the digital audio signal or digital video signal output from the audio visual decryption apparatus 167. The DA convertor 168 converts the digital audio signal or digital video signal into an analog audio signal or analog video signal. The digital signal output control part 170 converts the digital audio signal or analog audio signal into a preset output format (for instance, IEC60958, IEEE1394) and executes output control. The analog signal output control part 171 executes output control for the analog audio signal or analog video signal output by the DA convertor 168. The display part 172 displays an operating state. The system control part 173 reads the watermark CCI data and the digital CCI data, playback status information available from the signal processing part 164 and the encryption status information of the system stream available from the encryption/decryption apparatus 165, controls the digital signal output control part 170 and the analog signal output control part 171 and also controls the display part 172 and the mechanism control part 163 as well.
A digital playback operation of the optical disk player 174 having such a structure will now be described. The digital playback operation described below is an operation for a situation that DVD audio is recorded on the disk 160 and the DVD audio recorded on the disk 160 is played back.
The optical pickup 162 reads a signal recorded on the disk 160. While supplying the control signal to the mechanism control part 163, the signal processing part 164 retrieves data, corrects errors and extracts a system stream. The encryption/decryption apparatus 165 checks whether the system stream has been encrypted, and in the event that the system stream has been encrypted, decrypts the cipher and transfers the unencrypted system stream to the digital CCI decryption apparatus 166 and the audio visual decryption apparatus 167.
The audio visual decryption apparatus 167 extracts a digital audio signal or digital video signal out of the system stream, and decodes and transfers the signal to the watermark CCI decryption apparatus 169 and the digital signal output control part 170. As for the DVD audio, since video data such as a still picture can be attached to the DVD audio, the audio visual decryption apparatus 167 and the like process the digital audio signal or digital video signal.
The digital signal output control part 170 converts the digital audio signal or digital video signal into the preset output format (for instance, IEC60958, IEEE1394) and outputs the signal.
The digital CCI decryption apparatus 166 decodes digital CCI data out of the system stream and transfers the same to the system control part 173. The watermark CCI decryption apparatus 169 detects watermark CCI data out of the digital audio signal and transfers the same to the system control part 173.
The system control part 173 reads the digital CCI data and the watermark CCI data, and controls the digital signal output control part 170 and the mechanism control part 163 in accordance with these data. Further, the system control part 173 transfers operation display information to the display part 172.
With reference to FIG. 9, a description will now be given on an example of a copy control flow executed by the system control part 173 during playback of the conventional optical disk having the structure above.
First, the system control part 173 checks whether the system stream available from the encryption/decryption apparatus 165 has been encrypted (Step 1). In the event that the system stream has been encrypted, the system control part 173 checks whether there is digital CCI data (Step 2). When there is digital CCI data, the system control part 173 examines whether the digital CCI data is not “copy_freely” (Step 3). As shown in FIG. 7, the digital CCI of encrypted audio or video digital data indicates only “copy_one_generation” or “no_more_copy”, but not “copy_freely”. Hence, when the digital CCI data denotes “copy_freely”, the disk is determined an illegally copied disk. As a result, the system control part 173 controls both the digital signal output control part 170 and the analog signal output control part 171 and mutes both the digital signal output and the analog signal output (Step 4).
On the contrary, when it is determined at Step 3 that the digital CCI data does not denote “copy_freely”, the system control part 173 performs normal playback (Step 8).
Meanwhile, when it is determined at Step 1 that the system stream has not been encrypted and when it is determined at Step 2 that there is not digital CCI data, the system control part 173 reads whether there is watermark CCI available from the watermark CCI decryption apparatus 169 (Step 9). Next, with the presence of watermark CCI data, the system control part 173 inspects whether the watermark CCI data denotes “copy_freely” (Step 10). As shown in FIG. 7, normal playback is permitted only when the watermark CCI data denotes “copy_freely” (Step 12), whereas the disk is determined an illegal copy in the case of “copy_one_generation” and “no_more_copy”. In consequence, the system control part 173 controls both the digital signal output control part 170 and the analog signal output control part 171 and mutes both the digital signal output and the analog signal output (Step 11).
The system control part 173 recognizes the end of a playback unit (e.g., a whole piece of music) (Step 5) and returns back to Step 1 if the end has not come. When it is the end of a playback unit however, the system control part 173 determines whether the end of the whole disk has come (Step 6). When it is not the end of the whole disk, the system control part 173 sets the digital signal output control part 170 and the analog signal output control part 171 once again to normal output states and returns to Step 1. On the contrary, when it is the end of the whole disk, the system control part 173 ends the playback.
As described above, the first conventional technique secures copyright protection during playback of an optical disk.
Recording control utilizing electronic watermarking of the SDMI method according to “Amendment 3 to SDMI Portable Device Specification, Part I, Version 1.0” revised on Jun. 5, 2001 and issued by SECURE DIGITAL MUSIC INITIATIVE will now be described as a second conventional technique. Audio records and SD audio on Memory stick (registered trademark) comply with this SDMI control method.
The disclosure of “Amendment 3 to SDMI Portable Device Specification, Part I, Version 1.0” revised on Jun. 5, 2001 and issued by SECURE DIGITAL MUSIC INITIATIVE is incorporated herein by reference in its entirety.
Recording of SD audio is generally classified into two types. First, recording of an SDMI-protected content and second, recording of an SDMI-unprotected content. SDMI-protected contents, including the copy control information, are under protection by encryption according to the SDMI standard. Hence, SD audio recording of an SDMI-protected content must be in accordance with encrypted copy control information. On the other hand, in the case of an SDMI-unprotected content, which is content other than an SDMI-protected content, despite the existence of the copy control information attached to the content, the copy control information included in an electronic watermark embedded in the content needs be examined noting the possibility of tampering.
As for SD audio, a content to be recorded is compressed and encrypted into an SDMI-protected content. Further, in relation to the equipment identifier of SD audio equipment, a media identifier, etc., there is a restriction over the number of copies that can be made as SDMI-protected contents. In addition, a digital output is basically prohibited from SD audio equipment so that a digital copy (second-generation copy) will not be made on an ordinary digital medium (which may be an MD, a CD-R, etc.) which is not under the restriction described above. In other words, an SDMI-protected content is copy-prohibited other than on SD audio equipment. Hence, for recording of SD audio, only whether the copy control information of an input content denoting “no_more_copy” needs to be determined. Whether marking is “copy_one_generation” or “copy_freely” needs not be distinguished from each other.
Such an SDMI control method will now be described in further detail.
The SDMI control method is a control method of recording and playback of audio on a Memory stick, an SD memory card, etc.
FIG. 10 shows the outline of the SDMI control method. SD audio equipment employing the SDMI control method divides input signals into four types, i.e., a distributed input, a protected input, an unprotected input and an unencrypted content input, and performs different input processing on each of these.
First, a distributed input is inputting of content distributed via the Internet or the like. However, processing of content received as distributed input is processing outside the SDMI control method. A content received as a distributed input is distributed after it is encrypted usually by means of a different encryption scheme for each provider. For instance, using this encryption scheme, it is possible to set, for example, that up to three copies of the content can be made. Further, accounting or the like is also possible. Hence, in order to execute input processing of the content upon receipt of the content as a distributed input, using an encryption package corresponding to the provider, input processing of the content is carried out and purchase processing of the content is also executed. Thus distributed content is then recorded on an HDD, an SD card or the like with a priority given to an encrypted usage rule sent from the provider with the content, and applied to the content, i.e., in accordance with a rule set by an encryption scheme designed for each provider.
A protected input is inputting of a content transmitted by the IEEE1394-DTCP (Digital Transmission Content Protection) method.
IEEE1394 permits synchronous transmission of data in a high-speed bus system which is for serial transmission, and hence, realizes real-time transmission of audio visual data. As such, IEEE1394 is employed as an external interface in a wide spectrum of digital audio visual equipment including consumer digital audio visual equipment. The IEEE1394-DTCP method requires the authentication function and the key invalidation function in relation to data transmission over an IEEE1394 bus. As data which needs copyright protection such as audio visual data encrypted and transmitted, copyright protection is ensured. When content needs to be copyright-protected, at the time of transmission of the content, the content is encrypted and transmitted according to the IEEE1394-DTCP method, thereby protecting the copyright of the content.
Since content received as a protected input is transmitted by the IEEE1394-DTCP method, it is difficult to tamper the information regarding the copyright protection for the content. In short, since the information regarding the copyright protection for the content is reliable, when the content is input, control is implemented using digital CCI (digital copy control information).
That is, when the content is received as a protected input, the digital CCI of the content is detected, and whether to record on a medium is determined based on the detected digital CCI.
To be more specific, when the digital CCI of the content received as a protected input denotes “no_more_copy”, SD audio equipment complying with the SDMI control method does not record the content on a medium. On the contrary, when the digital CCI of the input content denotes “copy_freely” or “copy_one_generation”, this SD audio equipment encrypts the content and records the same on a medium, and as expressed in FIG. 10 as UPDATE DCCI (digital CCI), updates the digital CCI of the content to “no_more_copy” and performs CPRM encryption/recording. CPPM encryption/recording is encrypted recording based on an encryption rule defined in CPPM.
The reason why the SD audio equipment complying with the SDMI control method updates the digital CCI of the input content to “no_more_copy” and then records even when the digital CCI denotes “copy_freely” is because SD audio equipment complying with the SDMI control method is prohibited from outputting a digital output. Therefore, SD audio equipment does not comprise a digital output terminal.
Thus recorded content is processed as an SDMI-protected content.
An unprotected input is inputting of a content recorded on a CD or the like by SDMI control-compliant SD audio equipment in accordance with IEC958, which is a standard for transmitting such content over an optical cable, or inputting of such content as an analog signal. In the case of an unprotected input, because digital CCI could have been tampered, watermark CCI is detected and whether to permit recording is determined. In short, upon receipt of content as an unprotected input, SD audio equipment complying with the SDMI control method first detects watermark CCI, as expressed in FIG. 10 as DETECT WM (watermark). When the detected watermark CCI denotes “no_more_copy”, recording of the content received as an unprotected input does not take place. Meanwhile, when the detected watermark CCI denotes “copy_freely” or “copy_one_generation”, the content is CPRM encrypted and recorded on a medium, and the digital CCI of the recorded content is set to “no_more_copy”. The content recorded on the medium in this manner is handled as an SDMI-protected content when the content is to be played back from the medium. In this fashion, content received as a protected input or unprotected input is recorded on an HDD, an SD card or the like in accordance with a default usage rule. This rule applies a predetermined rule to an unprotected input such as a CD, a distributed content not bearing a usage rule and the like, that is, in accordance with a predetermined rule which may specify for instance that the number of check-outs is three or smaller.
An SDMI-protected content described above referring to a content which is transmitted in encrypted or otherwise protected form, is determined whether it can be recorded or not based on its digital CCI, and is encrypted by CPRM and recorded. Or the content which is determined whether it can be recorded or not based on its watermark CCI, at any stage of transmission, is passed screening using the watermark CCI, and is encrypted by CPRM and recorded.
An unencrypted content input is inputting of a content in unencrypted form as in the case of plaintext MP3 (MPEG Audio Layer III), and such a content is recorded in an unsecured area of a medium. However, an unencrypted content is outside the SDMI control method. A PC (personal computer) for instance can accept inputting of an unencrypted content. In short, a PC can receive content such as plaintext MP3 and record the same in an unsecured area of an SD memory card. Because permitting copying based on watermark CCI is not determined as for a content recorded in this manner, the content is called an SDMI-unprotected content. When an SDMI-unprotected content is to be output from SD audio equipment, watermark CCI is detected and playback is controlled in accordance with the SDMI control method. This will be described later.
Output processing in accordance with the SDMI control method will now be described.
Output processing in accordance with the SDMI control method includes processing of outputting to an SD memory card and analog output processing. During output processing in accordance with the SDMI control method, digital output processing is usually prohibited.
Processing of outputting to an SD memory card is managed by means of check-in/out. Check-in/out is processing of managing how many times one SDMI-protected content is checked out (recorded) onto, for example, an SD memory card, during recording of SDMI-protected contents recorded on a hard disk of a PC. When up to three check-outs of an SDMI-protected content onto SD memory cards is permitted for instance, after checking out the SDMI-protected content onto three SD memory cards, it is not possible to check out the SDMI-protected content onto other SD memory cards any more. However, when an SD memory card, onto which the SDMI-protected content has been checked out, is inserted in a PC and this SDMI-protected content is checked in onto the PC from the SD memory card inserted to the PC, it is possible to check out this SDMI-protected content onto yet another SD memory card. Upon check-in from the SD memory card to the PC, this SDMI-protected content gets deleted from the SD memory card. In this manner, the number of SD memory cards which will receive the SDMI-protected content is managed by means of check-outs.
Analog output processing is processing of outputting analog to ear phones, a speaker, etc. A content output through analog output processing is output usually at a speed of X1.5 or slower.
SD audio equipment complying with the SDMI control method can output an SDMI-protected content as analog independent of the values of the digital CCI, the watermark CCI, etc. In other words, because an SDMI-protected content was recorded in accordance with the copy control information, such as the digital CCI and the watermark CCI during recording, it is not necessary to perform playback control utilizing the copy control information again during playback. On the other hand, an unencrypted content recorded in an unsecured area of an SD memory card, namely, an SDMI-unprotected content is not recorded referring to watermark CCI, digital CCI or the like during recording. Hence, for playback, the watermark CCI is detected and playback control is performed based on the detected watermark CCI. Playback control is executed based on the watermark CCI because of possible tampering of the digital CCI.
Further, SD audio equipment complying with the SDMI control method does not comprise a digital output terminal so that a digital output will not be output as described above during playback of an SDMI-protected content, an SDMI-unprotected content, etc. For instance, SD audio equipment complying with the SDMI control method is not capable of outputting a digital output in accordance with IEC958.
Described below, as an example, is the recording control method for SD audio according to “Amendment 3 to SDMI Portable Device Specification, Part I, Version 1.0” revised on Jun. 5, 2001 and issued by SECURE DIGITAL MUSIC INITIATIVE. In short, an example of how content, received as unprotected input, is recorded as SD audio will be described. The description below corresponds to an operation in FIG. 10 of recording an SDMI-unprotected content received as an unprotected input onto an SD memory card, as expressed in FIG. 10 as UNPROTECTED INPUT.
FIG. 11 is a drawing which shows the timing of detecting an electronic watermark according to the second conventional technique. For detection of an electronic watermark, an audio signal lasting for fifteen seconds must be processed. This will be hereinafter referred to as an electronic watermark detection window.
FIG. 12 is a block diagram of a recording apparatus which utilizes electronic watermarking according to the second conventional technique. The recording apparatus is comprised of a content input terminal 801, an electronic watermark detection means 802 and a recording means 803. The electronic watermark detection means 802 is a means which detects an electronic watermark out of content. The recording means 803 is a means which records content.
The recording means 803 compresses content and records the same in encrypted form. When a control signal denoting “no_more_copy” is sent from the electronic watermark detection means 802, the content is deleted, including those portions which have been recorded so far.
FIG. 13 is a flow chart which shows the procedure in which the electronic watermark detection means 802 shown in FIG. 12 sends the control signal based on an electronic watermark of content. This will now be described with reference to FIG. 13.
First, upon receipt of a content start command, for the purpose of detecting an electronic watermark as a first trial within fifteen seconds from the start, the electronic watermark detection means 802 starts a first electronic watermark detection window, and within thirty seconds from the start, the first electronic watermark detection is completed (Step 1). The first electronic watermark detection may be started at the same time as the start of the content or any appropriate point within fifteen seconds from the start of the content. During recording of SD audio, the input content is compressed, encrypted and recorded. Although not shown in FIG. 12, the recording means 803 shown in FIG. 12 executes the compression/encryption processing at the same time as the electronic watermark detecting processing.
After the end of the first electronic watermark detection window, the electronic watermark detection means 802 confirms whether an electronic watermark has been found, that is, whether an electronic watermark detection flag is “1” (Step 2).
When it is found at (Step 2) that the electronic watermark detection flag is “1”, the electronic watermark detection means 802 confirms whether it is found the electronic watermark denotes “no_more_copy”, that is, whether the electronic watermark is “11” (Step 3).
When it is found at (Step 3) that the electronic watermark is not “11”, this content may be copied. Hence, at this stage, the electronic watermark detection means 802 terminates the detection of the electronic watermark and sends the control signal indicative of permission of copying to the recording means 803 (Step 8). The recording means 803 continues compression and encryption of the content.
On the contrary, when it is found at (Step 3) that the electronic watermark denotes “no_more_copy”, because copying of this content is prohibited, the electronic watermark detection means 802 sends the control signal, indicative of prohibition of copying to the recording means 803 (Step 9). The recording means 803 stops compression and encryption and deletes contents which have already been compressed and encrypted. Further, in the event that the recording apparatus records SD audio in the same housing as a CD player for instance, the recording apparatus may go to a next content during playback from a CD, stop playback or otherwise control. When receiving content from outside, the recording apparatus can not stop inputting of the content, and therefore, the recording apparatus may directly enter a standby state.
In contrast, when an electronic watermark is not found at (Step 2), the recording apparatus waits at any desired point at or after forty-five seconds (Step 4). The recording apparatus then performs a second electronic watermark detection, which is a detection of an electronic watermark as a second trial (Step 5).
The second electronic watermark detection is executed, because the first electronic watermark detection is performed near the top of an audio signal. Because playback of a tune has just started near the top of the audio signal, the audio signal is often at a low level. When the audio signal is often at a low level, detection of an electronic watermark is difficult. That is, when the level of the audio signal is low, the first electronic watermark detection often fails. As the second electronic watermark detection is performed after a while because of the first electronic watermark detection, it is likely that the level of the audio signal has risen before the second electronic watermark detection, despite the failure of the first electronic watermark detection. In this case, it is possible to more securely detect an electronic watermark. In other words, when an electronic watermark is detected during the first electronic watermark detection, the detection value is regarded valid. When no electronic watermark is detected during the first electronic watermark detection, it is possible that no electronic watermark was actually embedded or that electronic watermark detection has failed. Noting this, to reduce the risk of failure of the electronic watermark detection, the second electronic watermark detection is executed after a certain period of time.
As the second electronic watermark detection window ends, the electronic watermark detection means 802 confirms whether an electronic watermark has been found, that is, whether the electronic watermark detection flag is “1” (Step 6).
When it is found at (Step 6) that the electronic watermark detection flag is “1”, the electronic watermark detection means 802 confirms whether the electronic watermark thus found denotes “no_more_copy”, that is, whether the electronic watermark is “11” (Step 7).
When it is found at (Step 7) that the electronic watermark is not “11”, this content may be copied. Hence, the electronic watermark detection means 802 sends the control signal indicative of permission of copying to the recording means 803 (Step 8).
On the contrary, when it is found at (Step 7) that the electronic watermark denotes “no_more_copy”, because copying of this content is prohibited, the electronic watermark detection means 802 sends the control signal indicative of prohibition of copying to the recording means 803 (Step 9).
In contrast, when no electronic watermark is found at (Step 6), the recording apparatus decides that this content does not carry any electronic watermark and can therefore be copied. The electronic watermark detection means 802 therefore sends the control signal indicative of permission of copying to the recording means 803 (Step 8). The recording means 803 continues compression and encryption of the content to the end.
As described above, SD audio is under copyright protection by means of the recording control method according to “Amendment 3 to SDMI Portable Device Specification, Part I, Version 1.0” revised on Jun. 5, 2001 and issued by SECURE DIGITAL MUSIC INITIATIVE.
However, in the conventional structure described above, similar electronic watermark detection is involved in both the optical disk playback control described in relation to the first conventional technique and the SD audio recording control described in relation to the second conventional technique. In short, the optical disk playback control described in relation to the first conventional technique demands detection of all states of an electronic watermark. In contrast, it is not necessary to detect all states of an electronic watermark during the SD audio recording control described in relation to the second conventional technique. All states of an electronic watermark are nevertheless detected in the SD audio recording control of the second conventional technique. Thus, there is a problem that the efficiency is poor owing to excessive processing depending upon the specification of control.
That is, during the conventional SD audio recording control, copying of an SDMI-protected content is prohibited other than on SD audio equipment. Hence, although the copy control information of an input content denoting “no_more_copy” alone may be determined in the case of recording SD audio, all types of copy control of “no_more_copy”, “copy_one_generation” and “copy_freely” are detected from the copy control information of the input content. The SD audio recording control includes the excessive processing and is poorly efficient. Further, such a problem can occur during other recording control than that for SD audio. For example, a similar problem occurs during audio recording in accordance with the CPPM control method, the CPRM control method, etc.
Playback control of SD audio is similar. In other words, control is exercised such that as for playback of an SDMI-unprotected content, the content will not be played back when the copy control information denotes “no_more_copy”. However, the content will be played back when the copy control information denotes “copy_one_generation” or “copy_freely”. That is, whether it may alone be determined the copy control information of the input content denotes “no_more_copy”, control may be exercised such that playback will be stopped when the copy control information denotes “no_more_copy” but will be performed when the copy control information does not denote “no_more_copy”. Regardless of this, all types of copy control of “no_more_copy”, “copy_one_generation” and “copy_freely” are detected from the copy control information.
In other words, since all types of copy control expressed by the copy control information are detected during the conventional recording control or playback control, there is a problem that the efficiency is poor due to the excessive processing.